The present inventors have proposed a rotative arc welding device (Japanese laid-Open Publication No. 58-176073) which has given rise to many useful results by application to a narrow-groove welding. According to this welding device, the high-speed rotation of the welding arc promotes penetration at the side wall of the groove while also producing a concave bead shape suitable for multi-layer welding. The result is the significantly improved quality of the narrow groove welding. This welding device is hereafter referred to as the conventional welding device.
This conventional welding device has a vertically oriented rotary nozzle to the end of which is attached a tip having a wire supply opening offset from the axis outwardly, a power receiving plate secured to the upper end of the rotary nozzle and having a center wire inserting opening, a carbon brush the lower surface of which slides on the upper surface of said power receiving plate, a power supply plate secured to the upper surface of said carbon brush, and a wire inlet the lower end of which is passed through said power supply plate and said carbon brush so as to face to the upper surface of the wire inserting opening in said power receiving plate and having a wire insertion opening at the center attached to a supporting arm in turn extended from the main body of the device. The conventional welding device further includes a guide rod, the lower end of which is suspendedly mounted to said supporting arm is fitted into guide apertures in the power supply plate and in the carbon brush, a resilient member for pressing towards the power receiving plate the carbon brush which is fitted to the periphery of the guide rod and carrying the power supply plate, a wire feeder for feeding the welding wire through the wire inlet to the rotary nozzle, and a pair of shield gas nozzles provided on both sides of the rotative nozzle with its open side directing towards the end of the rotative nozzle.
The welding device of this type is shown schematically in FIG. 2. In the drawing, the numeral 1 denotes a gear box, the numeral 2 an electric motor, the numeral 3 an electrode, the npmeral 4 a wire inlet, the numeral 5 a shield gas nozzle base block, the numeral 6 a shield gas nozzle, the numeral 7 a wire feeder, the numeral 8 a welding wire, the numeral 9 a roller, the numeral 10 a wire feeding electric motor, the numeral 11 a power receiving plate, the numeral 12 a carbon brush, the numeral 13 a power supplying plate, the numeral 14 a guide plate, the numeral 15 a guide rod, the numeral 15 a spring, the numeral 16 a power supply cable, the numeral 17 a current supply cable terminal attachment opening, the numeral 18 a supporting arm and the numeral 19 a rotary postion sensor.
The above described welding device makes use of the carbon brush 12 for power supply since the electrode 3 itself is rotated. Thus the contact area for the carbon brush 12 must be procured for assuring a current supply capacity, while the rotative contact resistance of the carbon brush 12 need be considered, so that the current supply section or the electrical motor 2 is necessarily increased in size. This, however, has proved to be a hindrance when it is required to reduce the size of the welding device.